1. Field of the Invention
This invention relates to the cooling of electronic components mounted on a daughter card that is releasably connected to a circuit board and, more particularly, to the cooling of memory modules within a DIMM package attached to a circuit board.
2. Background of the Invention
Current computing systems, including personal computers and servers, contain system memory built in accordance with a packaging system called DIMM (Dual In-line Memory Modules).
Increases in the operating speed of microprocessors are pushing the requirements for the speed at which data is written to and read from system memory to levels not previously achieved. Furthermore, a long-term trend has been the realization of dramatic increases in the memory capacity that can occupy a particular space within a computing system. Both of these effects increase the rate at which heat must be dissipated, with the changes in memory speed that are occurring now driving the power that must be dissipated as heat for each DIMM memory module to levels twice as high as the levels achieved as recently as about two years ago. While cooling systems within personal computers and servers can currently dissipate 10 to 12 watts per DIMM module, it is anticipated that in the near future requirements will be made for dissipating 16 to 25 watts per DIMM module.
U.S. Pat. App. Pub. Ser. 2003/0076657 A1 describes a number of structures for dissipating heat from modules attached to elongated daughter cards, such as DIMM memory modules. Formed clamping structures extend over the modules, being held against the modules to facilitate the transfer of heat. In various configurations, heat is dissipated by structures also extending along both sides of the daughter card, such as elongated structures including corrugations or fins increasing the surface area available for heat dissipation. In one configuration, the clamping structure includes a number of resilient fingers extending outward from the end of the daughter card opposite the end at which it is removably connected from the circuit board, with these resilient fingers being staggered so that daughter cards so equipped can be installed in close proximity. These fingers are held in contact with a structure forming a thermal mass that absorbs heat generated by the modules. The daughter cards thus extend between the structure forming a thermal mass and the circuit board, so that the structure must be removed before one of the daughter cards can be removed or installed at one of the connectors on the circuit board. However, since daughter cards with memory modules are often removed and installed by the user of a computer system to upgrade the available memory, it is particularly important to retain the simplicity of removing and installing such daughter cards. Thus, what is needed is a system providing for the transfer of heat to a structure extending away from the daughter cards without requiring the removal of the structure before a daughter card can be removed or installed.
U.S. Pat. No. 6,025,992 also describes a circuit card unit comprising a memory card and an attached heat exchanger including a thin, flexible laminated strip of foil clad plastic, affixed in thermally conductive contact to each card module and extended therefrom to facilitate the removal of heat from the modules. In some embodiments, the exchanger strip extends from the modules on one side of the card to those on the other side in a self-supporting heat exchanger loop spaced over the memory card. In a somewhat more compact embodiment, the strip extends from modules on one card face, along the card itself, to the modules of the other card face. In still another embodiment, the heat exchanger strip extends from the modules of the card to a heat sink, such as the housing of the computer. What is needed is a heat exchanger fastened to the circuit card to carry heat from the circuit modules to a thermal bus in an arrangement that is connected and disconnected as the circuit card is connected and disconnected from the circuit board. Such a connection could be readily made and accurately re-established without concern for changes in the position of the circuit card relative to another structure in the computer, such as its housing.
The literature additionally includes a number of other examples of descriptions of apparatus, such as a thermal bus, for conducting heat away from the electronic components in which it is generated to other parts of a system. For example, U.S. Pat. No. 6,657,121 and U.S. Pat. App. Pub. Nos. 2003/0000721 A1 and 2004/0045730 A1 describe thermal energy management systems each having a heat spreading device that is operatively engaged with at least one semiconductor chip and a thermal bus operatively engaged with the heat spreading device to transport thermal energy from the heat spreading device to a heat sink. The heat spreading device includes a heat pipe, and the thermal bus includes a loop thermosyphon. U.S. Pat. No. 6,388,882 describes a system having a hierarchical scheme in which thermal management components are operatively engaged with individual portions of a system of electronic components and subsystems and in which the thermal management components are substantially only thermally driven, including, for example, heat transfer devices that have no moving parts, requiring no external power for their operation. Japanese Pat. No. 11087967 describes a system in which a heat exchanging part and a heat receiving part, separately arranged on a circuit board, are thermally connected by a heat pipe and by a ground layer of the circuit board. U.S. Pat. App. Pub. No. 2003/0035269 A1 describes a thermal bus for carrying heat from a die of an integrated circuit to a heat dissipating device such as a heat sink, forming a path for the removal of heat in addition to the traditional path through the surface of the die nearest the heat sink. The IBM Technical Disclosure Bulletin, August, 1990, pp. 158–160 describes thermally conductive and dissipative structures fabricated on a metal tape having the same format as a bonding tape, which are used for cooling VLSI chips. The structures all include a square central area that is attached to the chip and four generally trapezoidal wings that extend either up or down from the chip.
Again, what is needed is apparatus for transferring heat from circuit modules on a daughter card releasably attached to a thermal bus carrying heat away from the daughter card.